High Rock Lake is one of several impoundments on the Yadkin-Pee Dee river system in the North Carolina Piedmont. Flat Swamp Creek is, or was, a tributary to the Pee Dee River. After the High Rock reservoir filled Flat Swamp Creek became a narrow, northeast-trending arm to the larger lake. …

Ripples are periodic waveforms throughout the natural environment. These subaqueous asymmetrical wave ripples in sand under the Pee Dee River in North Carolina are created by oscillatory wave motions normal or slightly oblique to the shoreline.

Needle ice forms in porous, wet soil or sediment when the soil temperature is above freezing and the surface atmosphere temperature is below freezing. Permeability is important. Capillary action pulls water up toward the surface where the water freezes at the bases of growing ice crystals. The growing crystals are capable of lifting small particles and vegetation above the normal soil surface. This differential motion can thoroughly disaggregate and disrupt the upper several centimeters of the soil profile in temperate climates.

The images in this gallery were made in an elementary school yard where patches of bare soil are exposed. By the time I walked over the yard, the sun had melted most of the crystals except for those protected by shadows. Most of the single, larger grains on top of the crystals are coarse sand, perhaps around 2 mm (millimeters) in diameter.

This is a cluster of mostly standing needle ice crystals. Some of the crystals have toppled over as they began to melt. It’s likely that these crystals grew during a single freeze and growth event. In clusters with multiple growth events, there is often an intermediate layer of soil particles embedded across the axes of the crystals.Bundles of needle ice crystals in this cluster have fallen in different directions, probably oriented toward the least resistance or toward first melting. Some of the crystals have become detached fibers.

If you look closely, you can see that many of the needle ice individuals have longitudinal trains of bubbles. These may be air bubbles released as the crystals warm up and expand, or trapped during crystal growth. Whatever they are, the bubbles enhance the intricate internal structure of the crystals.As though swept over by a wind, these translucent, melting crystals all tilted in the same direction, roughly toward the east. It may be that eastern members of the cluster melted earlier in the day (this image was made at 1:29 PM), creating space for these crystals to fall.

Here are some fibrous crystals, all fallen but many retaining their sandy caps.Here is a very close view of a crystal forest with sand parapets overlooking great chasms.

Into the deep canyons you go.

Here is a streamlet of needle ice not quite frazil ice. This cluster did grow in a small gully, perhaps with a fair amount of water in the soil at the time of freezing. Several of these crystal streams have deep axial rifts. It could be that the thalwegs of these little streamlets were too saturated to allow crystal growth. It did not appear that the rift floors had been modified by crystal growth.This is the setting of the ice palaces. Not very impressive at this scale, is it? That’s because the most beautiful complexity in geology in the field is sometimes only visible in the Underworld – that diminutive realm within our vision but not often visited.

Needle ice in a loamy soil in a schoolyard near Salisbury, NC. The individual particles on top of the needles are coarse sand in size. Needle ice forms when soil water moves upward under capillary pressure and freezing when it contacts cold air. I will be posting a gallery of images with context on my blog soon. (The server is having intermittent problems right now.)